Katy Perry struggles with OCD.

The 'Roar' singer has obsessive compulsive disorder and finds herself inexplicably compelled to organise everything in alphabetical lists and eradicate all germs in her house with crazy cleaning rituals.

Referencing infamous OCD sufferer, movie mogul Howard Hughes, she told Z100 radio host Elvis Duran: ''I am so OCD. I always want to put things in alphabetical order. I am also a little Howard Hughes about germs.''

The pop star - who has been dating John Mayer since her divorce from Russell Brand - hopes she can go down in history as a musical legend like her personal icon, Sir Elton John.

Katy said: ''Elton John is a man that speaks his mind. Still, to this day, I love all his takes on life and opinions. He actually says what I feel a lot of people want to say, but we are just not that Elton John iconic level yet.

''He says the truth. I love his sense of humour and he says it how he sees it and his music, of course, is amazing. When you put out 30 records, you can say whatever the hell you want.''

The 28-year-old brunette also touched upon her difficult beginnings in the music industry and credited her international success to the power of making connections in the business.

She said: ''When I first started out, I was going over to every radio station, meeting all the people that direct all the different songs on the radio and having like bloomin' onions with them at Outback Steakhouse and introducing my music to them and making them feel like we have a connection and I still have many connections with those people.''